1. Field of the Invention
The present invention relates generally to treatment devices for use in heating and mixing various particulate material compositions and, more particularly, to an apparatus for continuously heating and mixing a number of particulate materials which are introduced into the apparatus at different locations.
2. Discussion of the Prior Art
It is known to employ a drum-mix plant for recycling remediated asphalt pavement (RAP) by introducing the RAP into a rotatable drum of the plant downstream of a burner flame and mixing the RAP with new aggregate particles which enter the drum adjacent the flame at the inlet of the drum. In this type of construction, it is possible to distance the RAP from the flame in order to reduce "blue smoke", an environmental problem arising from exposing the RAP to relatively high temperatures, e.g. greater than about 275 degrees Fahrenheit.
Typically, a dense veil of virgin aggregate particles are showered in front of the entering RAP particles in order to further shield the RAP particles from exposure to the flame. In other known constructions, mechanical shields are provided to carry out a similar function with the goal of reducing "blue smoke" to an acceptable level.
Certain drawbacks exist with each of these known constructions. For example, if the aggregate particles are used as a shield for the RAP particles, then special flighting is required within the drum or additional inlet openings are required to direct virgin material into the path of the flame to prevent exposure of the RAP particles to the flame. Further, where mechanical shields are used, supplementary hardware is required in addition to the hardware used to introduce the RAP particles into the drum in order to convert an existing drum plant into a plant capable of recycling RAP. Thus, such constructions are expensive to install and tend to render the plant less efficient than would be the case if the heat from the flame were more fully utilized in the heating process.
According to another known process, virgin aggregate is super-heated in a rotary dryer to a temperature of about 600.degree.-800.degree. F. and is then delivered to a separate batch or continuous mixer within which the aggregate is mixed with RAP particles. This composition then experiences a further treatment where it is mixed with liquid asphalt. However, because of the inefficient use of heat transfer in this known system, only a small percentage of RAP may be added to the aggregate. If larger percentages of RAP are added, the moisture within the RAP particles is not completely evaporated during mixing. Thereafter, continued evaporation of the moisture in the RAP particles after the composition has been delivered from the mixer causes unwanted cooling of the composition, and stripping of the liquid asphalt from the particles may result.
Another conventional use to which rotary dryers are put is for remediating soil which is contaminated with hydrocarbons and the like. During soil remediation, contaminated soil is introduced into the drum at the inlet of the drum and is conveyed in a direction either parallel or counter to the direction of flow of the hot gases. During conveyance of the soil, the hydrocarbons are evaporated and carried away with the hot gases to a conventional filtration system such as a baghouse, and the soil delivered from the outlet are lower in contaminates than when introduced into the drum.
One problem encountered in the use, of rotary dryers in the remediation of soil arises due to the collection of contaminated waste dust within the baghouse or filtration device through which the hot gasses and evaporated hydrocarbons pass after leaving the rotary dryer. It would be desirable to provide a means for remediating this waste dust without requiring additional machinery or expense beyond that required to operate the plant.